A great variety of water systems used presently require substantial ongoing water purity and contamination testing. For example, facilities such as municipal water supplies, beverage bottlers or medical facilities often require testing systems to protect the consumer or end user as well as to protect other equipment within the system. Still other systems operative in waste disposal or industrial water utilizing operations may be required to provide water testing of the discharged water as part of environmental monitoring or control operations.
On the one hand, periodic sample extraction and testing enjoys limited acceptance and may be employed in less critical operations, the most reliable practice for water testing and monitoring will use a continuous, or in-line testing system.
In one of the most common in-line testing systems the conductivity of the water or water solution is used an indication of water purity and contaminant content. The basic principle of such conductivity testing is relatively simple in that a pair of metal electrodes are immersed within the water or water solution and coupled to a source of electrical current. As the electrical current travels through the water or water solution between the electrodes, the conductivity or resistance of the water may be readily calculated to provide the desired indication of water purity. This conductivity testing has been found to yield excellent results and has wide scientific acceptance. Despite the great promise and advantages of such conductivity testing systems, several practical limitations and problems arise which has thus far precluded full realization of the benefits. Perhaps the most serious limitation and problem set arises due to the electrolytic properties of so-called aqueous solutions (solutions of water contaminated with mineral or metal materials or compounds). This set of properties is well known and arises when water-based solutions typical of virtually all water systems are subjected to electrical current between immersed electrodes. As the electrodes are energized, metal and mineral elements or other contaminants become ionized or charged and are carried to one or the other of the electrodes. At the electrode, the ionized or charged particles formed electrode deposits which over time coat and erode the electrodes reducing their efficiency and eventually rendering them useless. In addition, the coating or depositing action upon the electrodes often obstructs the water flow about the electrode and in certain structures may constrict the monitored water flow.
In efforts to meet these problems, practitioners in the art have employed exotic metal electrodes such as titanium, platinum, or carbon which tend to be less electrochemically active. Practitioners have also recommended frequent replacement of electrodes as well as the use of larger electrodes and AC current. An additional approach often tried is the provision of extra electrodes forming so-called sacrificial electrodes. Despite some limited improvement, such approaches have failed to provide the desired performance and reliability of electrical water testing systems.
The measurement of purity is a more subtle process than a simple measurement of conductivity. Purity measurement involves a more sensitive conductivity measurement, which may not be present in other measurement systems. For example, U.S. Pat. No. 3,474,330 to Thomas M. Dauphinee, which issued on Oct. 21, 1969 and is entitled "Conductivity Measuring Apparatus with Means for Comparing Sampled and Reference Voltages," discloses the use of a sensor and method which may operate up to a mile away from the measurement devices which operate the sensor. A sample cell is suspended in sea water from a ship, and water is allowed to move through the sample cell as the ship moves. In that case the utilization of DC current measurement was avoided for polarization effects, and AC current rejected due to the reactive interactions in the cable, phase problems and inability to accurately measure output over a long distance. The solution was the use of a square wave to provide and charging capacitors to measure the voltage average.
This technique may be adequate for sea water especially due to the long extension of equipment and the specialized probe employed. The problem occurs, which has heretofore been solved in the presence of multiple ground taps, as is encountered in conventional equipment. If a simple square wave device is used in such equipment, the grounding problems can alter the square wave. This, in turn will easily change the readings and most likely cause an unbalanced wave that can erode or plate the electrodes. Another problem with a simple square wave technique is that it is taking an average reading of the square wave voltages from the resistor and cannot use formulas developed and proven for actual reading using DC current measurement. Taking an average reading is not as accurate as taking an actual reading. Another problem with the technique is that depending on what frequency rates you use and the nature of the elements that are suspended in water, the phenomenon of frequency resonation can occur which can effect the average reading as well as the electrodes. It can also effect other monitoring or processing equipment connected to the distribution line. Any constant, continuously generated square wave form which does not exactly balance will tend to, on average, polarize the electrodes and cause problems.
The problems may range from electrochemical effects where one electrode has its metal ions dissolved into the surrounding water, to a chemical compilation of species in the water which collectively layer onto one or both electrodes. Even without a chopped signal, and where a completely regulated square wave can be provided, this signal can fall out of calibration. In fact, over time, one additional electron supplied to one electrode over the other per cycle can cause a major charge buildup.
There remains, therefore, a continuing need in the art for evermore improved water purity testing systems which exhibit greater reliability, longer electrodes and which avoid interfering with the primary water flow of the system, and which will defeat any buildup of charge or net charge presence on one electrode over another.